In recent years, as electronic devices become widely used, demands for current sensors which detect electric current are increasing. Particularly, as the size of the devices to be measured have been reduced, size reduction in the current sensors themselves is indispensable, and cost reduction is also required to be realized by simplifying the structure. Further, it is also required to detect electric current with higher accuracy and higher sensitivity, of course.
An example of a current sensor is disclosed in Japanese Patent Laid-Open No. 2008-20403 (Patent Document 1). FIG. 1A shows the schematic configuration of a magnetic sensor disclosed in Patent Document 1. As shown in FIG. 1A, the magnetic sensor is configured such that a measured current pattern 103, patterned on a printed wiring board 101, is covered with a magnetic core 102 having protruding portions 102a, and a magnetic sensor 104 is disposed at a position on the printed wiring board 101 facing the protruding portions 102a, whereby an output electric signal proportional to a measured current is acquired.
More specifically, when electric current flows in the measured current pattern 103, a magnetic field is generated by the current, and the magnetic field is intensified by the magnetic core 102. Then, as a strong magnetic field is generated in a portion between the protruding portions 102a of the magnetic core 102, that is, in the gap where the magnetic sensor 104 is disposed, it is possible to detect electric current by detecting this magnetic field. In particular, as the magnetic core 102 is processed to have U-shaped grooves in the right and left side faces, the magnetic core 102 is able to be disposed on the printed wiring board 101 without being divided. Further, as the magnetic sensor 104 is covered with the magnetic core 102, external magnetic noise can be blocked.
[Patent Document 1] JP 2008-20403 A
However, the magnetic core 102 of the above current sensor involves a problem that it detects external magnetic noise as well. Specifically, referring to FIG. 1B showing the magnetic core 102 disclosed in Patent Document 1, when an external magnetic field is generated in the vertical direction of the drawing, namely, in a direction indicated by arrows of solid lines, the external magnetic field may pass a part where the protruding portions 102a are formed while being intensified, as indicated by the arrows of dashed lines. As such, as the sensitivity of magnetic sensor becomes higher, it may detect external magnetic noise even in the case where no current flows in the measured current pattern 103. This causes a drop in the accuracy of current detection. Further, the above-described magnetic core 102 has a complicated shape with the protruding portions 102a inside, which also causes an increase in the component costs.